1. Field of the Invention
This invention relates to a camera permitting automatic exposure control (hereinafter will be called AE) and more particularly to a camera having an open aperture light measurement mode and a stop-down aperture priority AE mode.
2. Description of the Prior Art
The conventional camera of the kind having an open aperture light measurement mode and a stop-down aperture priotity AE mode permits mounting thereon an interchangeable lens adapted for open aperture light measurement and an interchangeable lens adapted for stop-down aperture light measurement. The conventional camera of this kind and the open aperture light measurement type interchangeable lens have been arranged as shown in FIG. 1 of the accompanying drawings. For an open aperture light measuring aperture priority AE mode and an open aperture light measuring shutter priority AE mode, the lens is provided with an automatic aperture control signal member which is arranged to be interlocked with the camera body and an aperture presetting signal member. A stop ring on aperture setting ring is arranged on the interchangeable lens to permit presetting a desired aperture value. The preset aperture value is transmittable to the camera body via a preset aperture signal member for TTL open apreture light measurement. The camera can be operated in an aperture priority AE mode by computing a shutter time value from the preset aperture value and a TTL open aperture light measurement value and by controlling the shutter time on the side of the camera body. When the stop ring is adjusted to an automatic operating position on the side of the interchangeable lens, the camera can be operated in a shutter priority mode with an aperutre value controlled by computing the aperture value from a shutter time value set on the side of the camera body and a TTL open aperture light measurement value and by controlling the above stated automatic aperture control signal member from the camera body.
Further details of arrangement of the conventional camera will be understood from the following description with reference to FIGS. 1 and 2: Referring to FIG. 1, a lens 202 is coupled with a camera body 204 by moving it in the direction of arrow .lambda.. The camera body 204 is provided with a mounting ring 276 on the side on which the above-stated lens 202 is to be mounted. Three separate flange parts 278A, 278B and 278C are arranged to protrude from the outer circumferential edge of the mounting ring 276. The mounting ring 276 is rigidly secured to the camera body 204 and is arranged in parallel with a film surface which is disposed perpendicularly to an opticl axis of the lens with the optical path of the lens being thus encompassed with the mounting ring. Since the mounting ring 276 is a sole member for coupling the lens assembly 202 with the camera body 204, inaccurate mounting and a secular change thereof would affect the image of an object to be formed on the film surface. In relation to the mounting ring 276, a clamp ring 210 is turnably arranged on the side of the lens assembly 202. Under the condition as shown in FIG. 1, when the lens assembly 202 is moved in the direction of arrow .lambda. to couple it with the body 204, the flange parts 278A, 278B and 278C of the mounting ring 276 are passable through notch parts 280A, 280B and 280C which are provided in a ring part. With these flange parts having passed these notch parts, when the clamp ring 210 is turned in the direction of arrow .phi., the flange parts 278A, 278B and 278C engage non-notched parts 282A, 282B and 282C of the clamp ring 210 to have the lens assembly 202 thus secured to the camera body 204.
On the mounting side of the lens assembly 202 at which the lens is to be mounted on the camera body 204, there are provided various mechanisms for control and exchange of information between the lens and the body. A lever 284 relates to the number of steps to which the aperture of the lens assembly 202 is stopped down from a maximum aperture position. The lever 284 is movable in the directions of arrows .psi. and .phi. along an annular slot 286 and is urged by a strong spring to move in the direction of arrow .phi.. However, when the lens assembly 202 is not mounted on the body 204 and is still in a preparative state as shown in FIG. 1, the lever 284 remains in a state of having been moved through the annular slot 286 in the direction of arrow .phi.. The lever 284 is released from this state when the clamp ring 210 is turned in the direction of arrow .phi. for mounting the lens assembly 202 on the camera body 204. In that case, the lever 284 which is a preset aperture signal member is caused by the urging force of the above-stated spring to move in the direction of arrow .phi. until the movement is restricted at a certain point. At this point, the lever 284 is in a position which corresponds to the number of stopped down steps of aperture from the maximum aperture position for a preset aperture value. The number of aperture stop down steps increases according as the lever 284 move further in the direction of arrow .phi. and becomes smaller according as the lever moves less in that direction. As mentioned in the foregoing, the lens assembly 202 permits presetting of an aperture value by means of an aperture setting ring 208. The movement restricted position of the lever 284 varies with the preset aperture value. Therefore, the lever 284 moves according as the preset aperture value varies. Accordingly, information on the number of stopped down steps of the preset aperture value which is set on the aperture setting ring 208 can be transmitted by the position of the lever 284 to the camera body 204.
When the aperture setting ring 208 has its mark 212 adjusted to an index 207, the lever 284 is in a position corresponding to a maximim stopped down position of the aperture of the lens assembly and is in a state of having been fully moved through the annular slot 286 by the urging force of the spring. The lever 284 is movable in the direction of arrow .psi., i.e. toward a smaller number of aperture steps, against the uring force of the spring from any position in which its further movement in the direction of arrow .phi. by the spring force is restricted. In other words, it is possible to obtain a desired aperture value by setting the lever 284 against the spring force at a desired postion without recourse to the aperture setting ring 208.
The lens assembly 202 is provided with a stop-down lever 288 which is a signal member for automatic aperture control; and a maxium aperture signal pin which protrudes to an extent corresponding to a minimum stop down value, i.e. the maximum aperture value of the photo taking lens assembly 202. This pin 290 is used for transmitting information on the maximum aperture value of the lens assembly to the camera body 204. A minimum aperture signal pin 291 is protruding to an extent corresponding to a maximum stop down value, i.e. the mimimum aperture value of the phototaking lens assembly 202 and is arranged to transmit the maximum stop down value of the lens assembly to the camera body 204. This minimum aperture signal pin 291 is used for detecting the controllable stopping down limit of the lens assembly 202 in carrying out an exposure control operation.
An AE pin 292 is arranged to protrude when the lens is in an automatic exposure control mode with the mark 212 which is provided on the aperture setting ring 208 adjusted to the index 207. In that mode, the AE pin 292 engages an AE detecting part which is interlocked with a switch S4 as will be further described later. In this instance, no aperture value is preset on the side of the lens assembly 202 and the aperture is controlled from the camera body according to information transmitted by the AE pin to the body 204.
Meanwhile, on the side of the camera body 204, there are provided various mechanisms which cooperate with the above-stated various mechanisms disposed on the side of the lens. These mechanisms on the side of the camera body includes a clamp mechanism which clamps the AE lever 294 at a suitable position determined on the basis of either an aperture value set by means of a dial or a controlled aperture value obtained through computation. The operation of this clamp mechanism brings the AE lever 294 to a stop at the clamped position. Accordingly, the movement of the lever 284 in the direction of arrow .phi. is restricted to a point which corresponds to the clamped position of the AE lever 294. Then, a number of stopping down steps is preset at that point. Therefore, the clamped position of the AE lever 294 is very important for determining a number of steps to which the aperture of the lens assembly 202 is to be stopped down. A mechanism or device which is arranged to detect the clamped position, therefore, must have a high degree of precision. This device is arranged in such a manner that: When the AE lever 294 moves in the direction of arrow .sigma. from a locked position which is a reference position, the extent of this move is converted into a number of pulses which are arranged to correspond to a number of stopping down steps of aperture. Then, a desired number of stopping down steps can be obtained by counting these pulses. For the purpose of this invention, a condition in which the AE lever 294 is locked in the reference position is called an AE charged condition and an operation to lock the AE lever 294 in the reference position is called an AE charging operation. Further, an operation to unlock the lever 294 from the reference position is called an AE discharge.
A maximum aperture value input pin 296 is arranged to receive information on the maximum aperture value of the lens assembly 202. The pin 296 abuts on the maximum aperture signal pin 290 of the lens assembly 202 to receive thereby a signal which corresponds to the protruding extent of the pin 290 and to the maxium aperture value of the lens assembly as shown in FIG. 2. This maximum aperture value input pin 296 is connected to a maximum aperture value signal generating ciucuit 87 which is arranged to convert the moving extent of the input pin 296 into a digital value as will be further described later herein. As a result, the information on the maximum aperture value of the lens assembly 202 is obtained in a digital value.
A minimum aperture value input pin 297 is arranged to receive information on the minimum aperture value of the lens assembly 202. The pin 297 abuts on the minimum aperture signal pin 291 of the lens assembly 202 to receive thereby a signal which corresponds to the protruding extent of the pin 291 and to the maximum stop down value, i.e. the minimum aperture value, of the lens assembly 202. This input pin 297 is connected to a device for converting the moving extent of the pin into a digital value, so that the maximum stop down value of the aperture of the lens assembly 202 is thus obtained in a digital value.
A side face of a stop drive lever 298 which faces in the direction of arrow .epsilon. is arranged to abut or confront one side of the stop down lever 288 of the lens assembly 202 which faces in the direction of arrow .OMEGA.. The lever 298 is arranged such that, before commencement of an exposure at the time of shutter release, the lever 298 is moved in the direction of arrow .epsilon. to drive the stop down lever 288 in the direction of arrow .nu., so that the aperture of the lens assembly 202 can be stopped down by the lever 284 from its full open position to a specific stopped down position. Upon completion of the exposure, the stop drive lever 298 moves in the direction of arrow .omega. to come back to its original position and thus brings the aperture of the lens assembly 202 back to the full open state thereof.
An AE detecting part 200 confronts the AE pin 292 of the lens assembly 202. The part 200 includes a switch S4. When the mark 212 is selected by the aperture setting ring 208 of the lens assembly 202, the AE pin 292 which protrudes at that instant causes the switch S4 of the AE detecting part 200 to turn off. When the mark 212 is not selected by the ring 208, the switch S4 turns on as the AE pin 292 does not protrude in that case. With the switch S4 arranged in this manner, the AE detecting part 200 produces a signal according to selection between automatic and manual operation modes.
As will be apparent from the description given above, the mark 212 of the aperture setting ring 208 must be adjusted to the index 207 in cases where the aperture value of the lens assembly 212 is to be controlled from the camera body 204. In view of this, hereinafter this mark 212 will be referred to as the AE mark.
The interchangeable lens which is adapted for open aperture light measurement is thus provided with the stop down lever 288 which is a signal member for automatic aperture control and another lever 284 which is a signal member for transmission of a signal representing a preset aperture value. With these member arranged to cooperate with the camera, the lens is capable of transmitting information to the camera.
However, in the conventional camera of the kind using the open aperture light measurement type interchangeable lens, it is necessary that the automatic aperture control signal member is brought, in response to a film winding operation, back to its initial position in which the aperture is full open and also to be moved, in response to a release operation of the camera, from the intial position in the direction in which the stopped down extent of the aperture increases. This necessity has presented the following problem: Since the automatic aperture control signal member is always kept in the full open aperture position upon completion of film winding, it has been impossible to confirm the depth of focus as the aperture is not stopped down in spite of an attempt to actually stop down the aperture prior to a photo-taking operation. To solve this problem, Japanese Laid-Open Patent Application No. SHO 52-91426 has disclosed a camera, wherein the aperture can be stopped down by manually driving the stop drive lever 298 even when an open aperture light measurement type interchangeable lens is mounted on the camera. This camera of the prior art, however, has necessitated not only complex mechanical arrangement but also an operation which is too complex for a beginner photographer.
Meanwhile, an interchangeable lens of the kind adapted for stop down aperture light measurement is not provided with the above-stated automatic aperture control signal member nor the preset aperture signal member though the lens is arranged in a manner similar to the interchangeable lens adapted for open aperture light measurement as described in the foregoing. Therefore, no aperture information is transmitted to the camera even the interchangeable lens is set at a desired aperture value by means of the aperture setting ring thereof and TTL open aperture light measurement cannot be accomplished and the aperture of the lens is merely arranged to be stopped down. With a stop down aperture light measurement type interchangeable lens mounted thereon, therefore, the camera is incapable of performing a photo-taking operation neither in the open aperture light measuring, aperture priority AE mode nor in the open aperture light measuring, shutter priority AE mode. For automatic exposure control photographing (AE photographing), the lens of this kind permits photographing solely in a stop down aperture priority AE mode in which a shutter itme value is determined by computation on the basis of a light measurement value obtained from light measurement carried out with the aperture of the interchangeable lens stopped down and information of the sensitivity of the film in use.
Further, in the open aperture light measurement type interchangeable lens, the maximum aperture value of the lens is arranged to be represented by the height of the full-open or maximum aperture signal pin 290 as shown in FIG. 2 and to have information thereon taken in by the full-open or maximum aperture signal input pin 296 arranged on the side of the camera body. Meanwhile, in the case of the stop down aperture light measurement type interchangeable lens, the position or height of the end face of the lens corresponding to the position of the full-open aperture signal pin 290 as shown in FIG. 2 is arranged to represent F 5.6 irrespective of the maximum aperture value of the lens. In the stop down aperture light measurement type lens, unlike the open aperture light measurement type lens, the mark 212 is not selected by the aperture setting ring 208 of the lens assembly 202 and there is provided nothing that corresponds to the AE pin 292. Accordingly, in that case, the AE detecting part 200 is never pushed inward by such a pin. The stop down aperture light measurement type interchangeable lens and the open aperture light measurement type interchangeable lens can be distinguished from each other by the following condition:
In the case of the stop down aperture light measurement type interchangeable lens, the height corresponding to the position of the above-stated full open or maximum aperture signal pin 290 corresponds to F 5.6; and the AE detecting part 200 is never pushed in. The camera can be judged to have a stop down aperture light measurement type interchangeable lens mounted thereon in case where these conditions are satisfied and to have an open aperture light measurement type interchangeable lens mounted thereon in case these conditions are not satisfied.